1. Field of the Invention
The present invention relates to a hands-free device that enables a hands-free telephone conversation to take place in a car, and especially to a hands-free device that outputs voice of the other party of a telephone conversation from speakers provided in a car.
2. Description of the Prior Art
Conventionally, a hands-free system that enables a telephone conversation to take place without a driver having a cellular phone in his/her hand (hereafter, a hands-free telephone conversation is used in this sense) is proposed (the Japanese Laid-Open Patent Application No. H5-130010).
FIG. 1 is a diagram that shows a structure of a conventional hands-free system.
The conventional hands-free system shown in FIG. 1 comprises, for example, a driver's cellular phone 90, which the driver brings into a car, and a hands-free device 110 that is installed in the car, communicates with and controls the cellular phone 90, outputs a voice of the other party of a telephone conversation, and transmits the driver's voice to the other party of the telephone conversation.
The hands-free device 110 comprises a communication unit 111 that communicates with the cellular phone 90, a control unit 112 that controls the communication unit 111, a microphone 115 that captures a driver's voice and outputs driver's voice signals indicating the voice, a speaker 113d that is set up near the driver's seat 116a, a speaker 113a that is set up near a front passenger's seat 116b, two speakers 113b and 113c that are set up near a back seat 116c, and an amplifier 114 that inputs telephone conversation voice signals indicating the other party's voice of a telephone conversation outputted from the communication unit 111, amplifies the telephone conversation voice signals and outputs them to four speakers 113a-113d. 
The cellular phone 90 comprises a cellular phone main body 91 that can communicate with another telephone and enables the driver to converse by the telephone, and a hands-free communication unit 92 that communicates with the communication unit 111 of the hands-free device 110, controlled by the cellular phone main body 91.
This hands-free communication unit 92 of the cellular phone 90 is connected with the communication unit 111 of the hands-free device 110 wirelessly.
FIG. 2 is a block diagram that shows the functions of the above-mentioned cellular phone main body 91 of the cellular phone 90.
The cellular phone main body 91 comprises, as FIG. 2 shows, a telephone communication unit 91b that communicates with another telephone through a telephone line network 613, a cellular phone microphone 91c, a cellular phone speaker 91d, and main control unit 91a that controls the cellular phone microphone 91c, the cellular phone speaker 91d, and the telephone communication unit 91b. 
When this cellular phone 90 is not connected with the hands-free device 110, it enables the user of cellular phone 90 to communicate by telephone with the user of another telephone by using the cellular phone speaker 91d and the cellular phone microphone 91c that are equipped with the cellular phone main body 91.
In other words, the main control unit 91a has the cellular phone microphone 91c capture the user's voice of the cellular phone 90, and has the telephone communication unit 91b transmit signals indicating the voice to another telephone through the telephone line network 613. Then, when the telephone communication unit 91b receives the telephone conversation voice signals indicating the other party's voice of the telephone conversation who uses the other telephone, the main control unit 91a transmits the telephone conversation voice signals to the cellular phone speaker 91d, and has the cellular phone speaker 91d output the other party's voice of the telephone conversation.
When a driver brings the cellular phone into a car and connects the cellular phone 90 with the hands-free device 110, the above-mentioned hands-free system comprising the hands-free device 110 and the cellular phone 90, has the microphone 115 of the hands-free device 110 capture the driver's voice, has the speakers 113a-113d output the other party's voice of the telephone conversation, without the cellular phone microphone 91c and the cellular phone speaker 91d performing the above-mentioned operations, and enables the driver to make a hands-free telephone conversation.
To be more specific, the telephone communication unit 91b of the cellular phone main body 91 is called by the other telephone through the telephone line network 613, and outputs incoming call signals indicating an incoming call to the main control unit 91a, which has the hands-free communication unit 92 transmit the incoming call signals to the communication unit 111 of the hands-free device 110.
When the control unit 112 of the hands-free device 110 realizes that the communication unit 111h as received the incoming call signals, and inputs from the outside an answering instruction signal that instructs to answer the incoming call, it has the communication unit 111 transmit the answering instruction signal to the hands-free communication unit 92 of the cellular phone 90.
When the main control unit 91a of the cellular phone main body 91 realizes that the hands-free communication unit 92 has received the answering instruction signal, it controls the telephone communication unit 91b so that the telephone communication unit 91b can receive the telephone conversation voice signals transmitted by the other telephone.
Then, the main control unit 91a has the hands-free communication unit 92 transmit the telephone conversation voice signals received by the telephone communication 91b to the communication unit 111 of the hands-free device 110. The control unit 112 of the hands-free device 110 has the communication unit 111 transmit the telephone conversation voice signals to the amplifier 114. As a result, the four speakers 113a-113d in the car output the other party's voice of the telephone conversation.
Furthermore, when the control unit 112 of the hands-free device 110 realizes that the communication unit 111h as received the incoming call signals and inputs from the outside the answering instruction signal that instructs to answer the incoming call, the control unit 112 has the communication unit 111 transmit the driver's voice signals outputted from the microphone 115 to the hands-free communication unit 92 of the cellular phone 90. The cellular phone main body 91 transmits the driver's voice signals received by the hands-free communication unit 92 to the other telephone through the telephone line network 613.
Thus, under the hands-free device 110 of the conventional hands-free system, the microphone 115 captures the driver's voice, the cellular phone 90 transmits the driver's voice signals indicating the voice to the other telephone, and at the same time, based on the telephone conversation signals received by the cellular phone 90, the speakers 113a-113d output the other party's voice of the telephone conversation, and the driver can have a hands-free conversation.
However, under the above-mentioned hands-free device 110 of the conventional hands-free system, because the other party's voice during the telephone conversation propagates within the whole body of the car, a fellow passenger hears the voice of the telephone conversation when there is a fellow passenger, and therefore, there is a problem that the privacy of the driver and the other party of the telephone conversation cannot be protected.
Additionally, in order that only the driver hears the telephone conversation, for example, a hands-free device under which a speaker with directional characteristic to the output direction is set up near the driver's seat with the output direction aimed at the driver is proposed (Japanese Laid-Open Patent Application No. H5-92741). However, in this case, in contrast to the above description, because the voice of the other party of the telephone conversation does not propagate within the whole body of the car, the sound quality of the voice during the telephone conversation is poor. When there is a fellow passenger, it cannot be helped from the view point of protecting the privacy, but the driver wants to hear the other party's voice during the telephone conversation with high quality when there is no fellow passenger.